Light emitting semiconductor structure

ABSTRACT

The invention provides a light emitting semiconductor structure, which includes a substrate; a first LED chip formed on the substrate; an adhesion layer formed on the first LED chip; and a second light emitting diode chip formed on the adhesion layer, wherein the second LED chip has a first conductive wire which is electrically connected to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending application Ser. No.13/078,541, filed on Apr. 1, 2011, for which priority is claimed under35 U.S.C. §120, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting semiconductorstructure and in particular relates to a light emitting semiconductorstructure with at least two LED chips.

2. Description of the Related Art

Because light emitting semiconductor structure have several advantagesover conventional lamps, such as a long lifetime, a small size, lowpower consumption, high response speed, etc., considerable researchattention has been recently focused on development thereof.

Conventionally, one way to generate a white light emitting semicondcutorstructure is to coat or fill a yellow phosphor on a blue LED chip. Theblue light emitted by the LED chip is then mixed with the complimentaryyellow light from phosphor to generate white light.

The other way to generate a white light emitting semiconductor structureis to mix different colors emitted from a plurality of the LEDs toproduce a white light emitting diode. U.S. Pat. No. 7,005,667 disclosesa light emitting diode, wherein a blue LED chip is arranged parallel toa blue-complimentary LED chip (such as yellow LED chip) to generatewhite light. However, two LEDs are arranged in the same plane and thusoccupy too much area. Therefore, the package size of the light emittingsemiconductor structure can not be reduced.

Therefore, there is a need to develop a light emitting semiconductorstructure which has a small package size to simplify the design of thesecondary optical lens in the subsequent steps.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a light emitting semiconductor structure,comprising: a substrate; a first LED chip formed on the substrate; anadhesion layer formed on the first LED chip; and a second light emittingdiode chip formed on the adhesion layer, wherein the second LED chip hasa first conductive wire which is electrically connected to the substrate

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1A to 1B show cross-sectional schematic representations of a lightemitting semiconductor structure in accordance with embodiments of theinvention;

FIG. 2 shows a cross-sectional schematic representation of a lightemitting semiconductor structure in accordance with a second embodimentof the invention;

FIG. 3 shows a cross-sectional schematic representation of a lightemitting semiconductor structure in accordance with a third embodimentof the invention;

FIG. 4A to 4B show cross-sectional schematic representations of a lightemitting semiconductor structure in accordance with a fourth embodimentof the invention; and

FIG. 5 shows a cross-sectional schematic representation of a lightemitting semiconductor structure in accordance with a fifth embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

The following descriptions of FIG. 1 to FIG. 5 are used to describe alight emitting semiconductor structure of the invention. The drawingsare idealized representations for better illustration of the structureof the invention, and various elements are not necessarily shown toscale.

FIG. 1A shows a cross-sectional schematic representation of anembodiment of a light emitting semiconductor structure 10. The lightemitting semiconductor structure 10 comprises two light emitting diodechips which are vertically stacked and emit different colors of light toproduce a white light.

The light emitting semiconductor structure 10 comprises a substrate 100,a first LED chip 200, an adhesion layer 300 and a second LED chip 400,wherein the first LED chip 200 is formed on the substrate 100, theadhesion layer 300 is formed on the first LED chip 200, and the secondLED chip 400 is formed on the adhesion layer 300. The second LED chip400 has a first conductive wire 450 which is electrically connected tothe substrate 100.

The material of the substrate 100 comprises silicon substrate, ceramicsubstrate or lead frame. The first LED chip 200 or the second LED chip400 comprises a sub-substrate, an N-type conductive layer, an activelayer and a P-type conductive layer. The adhesion layer 300, such astransparent adhesive glue, is used to combine the first LED chip 200 andthe second LED chip 400 together. The first LED chip 200 comprises afirst pad 210 and a second pad 212 which are electrically connected tothe substrate 100. Additionally, a connective layout (not shown) isformed between the substrate 100 and the firs pad 210 and second pad212, and the conductive layout may be a conventional adhesive or metalbump (such as solder, gold or aluminum bumps).

FIG. 1B shows a detailed schematic representation of the light emittingsemiconductor structure 10 of FIG. 1A. A first conductive typesemiconductor layer 204, an active layer 206 and a second conductivetype semiconductor layer 208 are in sequence formed on a sub-substrate202. The first pad 210 is formed on the first conductive type,semiconductor layer 204, and the second pad 212 is formed on the secondconductive type semiconductor layer 208.

The first conductive type semiconductor layer 204 or the secondconductive type semiconductor layer 208 are made of a III-V compoundsemiconductor. In one embodiment, the first conductive typesemiconductor layer 204 is an N-type nitride, and the second conductivetype semiconductor layer 208 is a P-type nitride. In another embodiment,the first conductive type semiconductor layer 204 is a P-type nitride,and the second conductive type semiconductor layer 208 is an N-typenitride. The first conductive type semiconductor layer 204 mayoptionally be doped with silicon (Si) and the second conductive typesemiconductor layer 208 may optionally be doped with zinc (Zn) ormagnesium (Mg).

Likewise, a first conductive type semiconductor layer 404, an activelayer 406 and a second conductive type semiconductor layer 408 are insequence formed on a sub-substrate 402. The third pad 410 is formed onthe first conductive type semiconductor layer 404, and the fourth pad412 is formed on the second conductive type semiconductor layer 408.

In FIG. 1A, the first LED chip 200 is electrically connected to thesubstrate 100 by a flip-chip method, and more specifically, the firstLED chip 200 is electrically connected to the substrate 100 by the firstpad 210 and the second pad 212. The second LED chip 400 is electricallyconnected to the substrate 100 by a wire bonding method, and morespecifically, the second LED chip 400 is electrically connected to thesubstrate 100 by the third pad 410 and the fourth pad 414 through thefirst conductive wire 450.

The first LED chip 200 and the second LED chip 400 may be electricallyconnected in parallel or in series with each other. In one embodiment,the first LED chip 200 has a P-type first pad 210P and an N-type secondpad 212N, and the second LED chip 400 has a P-type third pad 410P and anN-type fourth pad 412N, and the P-type first pad 210P is electricallyconnected to the P-type third pad 410P by an electrical interconnectionbuilt on the substrate and the N-type second pad 212N is electricallyconnected to the N-type fourth pad 412N by another electricalinterconnection built on the substrate. Thus, the first LED chip 200 andthe second LED chip 400 are electrically connected in parallel with eachother.

In another embodiment, the first LED chip 200 has a P-type first pad210P and an N-type second pad 212N, and the second LED chip 400 has anN-type third pad 410N and a P-type fourth pad 412P, and the P type firstpad 210P is electrically connected to the N-type third pad 410N by anelectrical interconnection built on the substrate and the N-type secondpad 212N is electrically connected to the P-type fourth pad 412P byanother electrical interconnection built on the substrate. Thus, thefirst LED chip 200 and the second LED chip 400 are electricallyconnected in series with each other.

Note that in FIG. 1 the first LED chip 200 and the second LED chip 400are combined by the adhesion layer 300. Thus, the first LED chip 200 andthe second LED chip 400 are insulated from each other by the adhesionlayer 300. More specifically, the first LED chip 200 has a first surface200 a contacting the adhesion layer 300, the second LED chip 400 has asecond surface 400 a contacting the adhesion layer 300, and the firstsurface 200 a is insulated from the second surface 400 a by the adhesionlayer 300. In other words, there is no electrical connection between thefirst surface 200 a and the second surface 400 a. Because the firstsurface 200 a is insulated from the second surface 400 a, the electricalconnection relationship between the first LED chip 200 and the secondLED chip 400 depends on the electrical interconnections built on thesubstrate.

In one embodiment, the first LED chip 200 emits blue light and thesecond LED chip 400 emits yellow light. The blue light is mixed with theyellow light to generate white light. In another embodiment, the firstLED chip 200 emits yellow light and the second LED chip 400 emits bluelight.

FIG. 2 shows a cross-sectional schematic representation of a secondembodiment of a light emitting semiconductor structure 20, wherein likeelements are identified by the same reference numbers as in FIG. 1A, andare thus omitted for clarity. The difference between FIG. 2 and FIG. 1Ais that a plurality of second LED chips 400 shown in FIG. 2. In FIG. 2,there are at least two second LED chips 400 formed on the adhesion layer300, and thus a size of these second LED chips 400 is smaller than asize the first LED chip 200. The advantage of the second embodiment isthat these second LED chips 400 may be arranged in any shape, such ascircular, triangular, rectangular, or irregular shapes (from a top viewof the LED 20, not shown in the Figure), depending on actual applicationneeds.

FIG. 3 shows a cross-sectional schematic representation of a thirdembodiment of a light emitting semiconductor structure 30, wherein likeelements are identified by the same reference numbers as in FIG. 1A, andare thus omitted for clarity. The difference between FIG. 3 and FIG. 1Ais that the first LED chips 200 is electrically connected to thesubstrate 100 by a wire bonding method in FIG. 3. As shown in FIG. 3, asilver glue 150 is formed on the substrate 100 and the first LED chip200 is formed on the silver glue 150. Additionally, the first LED chip200 has a second conductive wire 250 which is electrically connected tothe substrate 100. Note that the first LED chip 200 has the secondconductive wire 250 which occupies some surface areas of the first LEDchip 200, and thus a size of the second LED chip 400 is smaller than asize the first LED chip 200.

Note that in the third embodiment, the first LED chip 200 and the secondLED chip 400 are combined by the adhesion layer 300. Thus, the first LEDchip 200 and the second LED chip 400 are insulated from each other bythe adhesion layer 300. More specifically, the first LED chip 200 has afirst surface 200 a contacting the adhesion layer 300, the second LEDchip 400 has a second surface 400 a contacting the adhesion layer 300,and the first surface 200 a is insulated from the second surface 400 aby the adhesion layer 300. In other words, there is no electricalconnection between the first surface 200 a and the second surface 400 a.Because the first surface 200 a is insulated from the second surface 400a, the electrical connection relationship of the first LED chip 200 andthe second LED chip 400 depends on the electrical interconnections builton the substrate.

FIG. 4A shows a cross-sectional schematic representation of a fourthembodiment of a light emitting semiconductor structure 40, wherein likeelements are identified by the same reference numbers as in FIG. 1A, andare thus omitted for clarity. The difference between FIG. 4A and FIG. 1Ais that an additional third LED chip 600 is shown in FIG. 4A. A secondadhesion layer 500 is formed on the second LED chip 400, and a third LEDchip 600 is formed on the second adhesion layer 500. Furthermore, thethird LED chip 600 has a third conductive wire 650 which is electricallyconnected to the substrate 100 by a wire bonding method.

Note that the advantage of the third embodiment is that severalmonochromatic colors emitted by the LED chips 200, 400, and 600 aremixed to improve the color rendering index (CRI) of the LED 40.

Additionally, in FIG. 4A the second LED chip 400 and the third LED chip600 are combined by the second adhesion layer 500. Thus, the second LEDchip 400 and the third LED chip 600 are insulated from each other by thesecond adhesion layer 500. More specifically, the second LED chip 400has a third surface 400 b contacting the second adhesion layer 500, thethird LED chip 600 has a fourth surface 600 a contacting the secondadhesion layer 500, and the third surface 400 b is insulated from thefourth surface 600 a by the second adhesion layer 500. In other words,there is no electrical connection between the third surface 400 b andthe fourth surface 600 a.

In one embodiment, the first LED chip 200, the second LED chip 400 andthe third LED chip 600 emit three different colors of light. The threedifferent colors of light comprise blue light, green light and redlight. Thus, there are six permutations. In one embodiment, the firstLED chip 200 emits blue light, the second LED chip 400 emits green lightand the third LED chip 600 emits red light. In another embodiment, thefirst LED chip 200 emits green light, the second LED chip 400 emits bluelight and the third LED chip 600 emits red light. In yet anotherembodiment, the first LED chip 200 emits red light, the second LED chip400 emits green light and the third LED chip 600 emits blue light. Inone embodiment, the first LED chip 200 emits green light, the second LEDchip 400 emits red light and the third LED chip 600 emits blue light.

In another embodiment, the first LED chip 200, the second LED chip 400and the third LED chip 600 emit three different colors of light. Thethree different colors of light comprise blue light, yellow light andred light. Thus, there are six permutations. In one embodiment, thefirst LED chip 200 emits blue light, the second LED chip 400 emitsyellow light and the third LED chip 600 emits red light. In anotherembodiment, the first LED chip 200 emits yellow light, the second LEDchip 400 emits blue light and the third LED chip 600 emits red light. Inyet another embodiment, the first LED chip 200 emits red light, thesecond LED chip 400 emits yellow light and the third LED chip 600 emitsblue light. In one embodiment, the first LED chip 200 emits blue light,the second LED chip 400 emits red light and the third LED chip 600 emitsyellow light.

FIG. 4B shows a modified fourth embodiment of the light emittingsemiconductor structure 40, wherein the third LED chip 600 is formed onthe adhesion layer 300 rather than the second adhesion layer 500. Inother words, the third LED chip 600 is formed on the first LED chip 200.Likewise, the third LED chip 600 has a third conductive wire 650 whichis electrically connected to the substrate 100 by a wire bonding method.More specifically, the first LED chip 200 has a first surface 200 acontacting the adhesion layer 300, the third LED chip 600 has a fifthsurface 600 b contacting the adhesion layer 300, and the first surface200 a is insulated from the fifth surface 600 b by the adhesion layer300.

FIG. 5 shows a cross-sectional schematic representation of a fifthembodiment of a light emitting semiconductor structure 50, wherein likeelements are identified by the same reference numbers as in FIG. 1A, andare thus omitted for clarity. The difference between FIG. 5 and FIG. 1Ais that an additional phosphor 700 is coated on the first LED chip 200and the second LED chip 400. A white light is generated by mixing atleast two LED chips 200, and 400 and the phosphor 700.

In one embodiment, one of the first LED chip 200 or the second LED chip400 emits blue light, the other emits red light, and the phosphor 700emits yellow light.

In another embodiment, one of the first LED chip 200 or the second LEDchip 400 emits blue light, the other emits yellow light, and thephosphor 700 emits green light.

In yet another embodiment, the phosphor 700 is coated on third LED chip600 of FIG. 4A. Thus, a white light is generated by mixing three LEDchips 200, 400, and 600 and the phosphor 700. Note that themonochromatic color lights emitted by the LED chips or the phosphor arenot limited to the above descriptions; thus, those skilled in the artmay adjust the colors of the LED chips or phosphor according to actualapplication needs.

The invention provides a light emitting semiconductor structure in whichat least two LED chips are vertically stacked. Compared with the LEDchips arranged in the same plane, the semiconductor structure of theinvention has a smaller package size. Thus, in sequential steps, asecondary optical lens may be easily designed. Additionally, severalmonochromatic colors emitted by the LED chips are mixed to generate andto improve the color rendering index (CRI) of the semiconductorstructure of the invention.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1-5. (canceled)
 6. A light emitting semiconductor structure lightemitting semiconductor structure, comprising: a substrate; a first LEDchip formed on the substrate; an adhesion layer formed on the first LEDchip; a second LED chip formed on the adhesion layer, wherein the secondLED chip has a first conductive wire which is electrically connected tothe substrate; a second adhesion layer formed on the second LED chip;and a third LED chip formed on the second adhesion layer.
 7. The lightemitting semiconductor structure as claimed in claim 6, wherein thesecond LED chip has a third surface contacting the second adhesionlayer, the third LED chip has a fourth surface contacting the secondadhesion layer, and the third surface is insulated from the fourthsurface.
 8. The light emitting semiconductor structure as claimed inclaim 6, wherein the third LED chip has a third conductive wire which iselectrically connected to the substrate.
 9. The light emittingsemiconductor structure as claimed in claim 6, wherein the first LEDchip, the second LED chip and the third LED chip emit three differentcolors of light.
 10. The light emitting semiconductor structure asclaimed in claim 9, wherein the three different colors of lightcomprises blue light, green light and red light.
 11. The light emittingsemiconductor structure as claimed in claim 9, wherein the threedifferent colors of light comprises blue light, yellow light and redlight.
 12. The light emitting semiconductor structure as claimed inclaim 6, further comprising a phosphor coated on the first LED chip, thesecond LED chip and the third LED chip.
 13. The light emittingsemiconductor structure as claimed in claim 6, further comprising athird LED chip formed on the adhesion layer.
 14. The light emittingsemiconductor structure as claimed in claim 13, wherein the first LEDchip has a first surface contacting the adhesion layer, the third LEDchip has a fifth surface contacting the contacting the adhesion layer,and the first surface is insulated from the fifth surface.
 15. The lightemitting semiconductor structure as claimed in claim 13, wherein thethird LED chip has a third conductive wire which is electricallyconnected to the substrate.
 16. The light emitting semiconductorstructure as claimed in claim 13, wherein the first LED chip, the secondLED chip and the third LED chip emit three different colors of light.17. The light emitting semiconductor structure as claimed in claim 16,wherein the three different colors of light comprises blue light, greenlight and red light.
 18. The light emitting semiconductor structure asclaimed in claim 16, wherein the three different colors of lightcomprises blue light, yellow light and red light.
 19. The light emittingsemiconductor structure as claimed in claim 13, further comprising aphosphor coated on the first LED chip, the second LED chip and the thirdLED chip.
 20. The light emitting semiconductor structure as claimed inclaim 6, further comprising a phosphor coated on the first LED chip andthe second LED chip.